"arcane rituals; arcane knowledge; The professor’s lecture was full of arcane references.; The manuscript contained arcane symbols no one could decipher.; He had an arcane knowledge of ancient rituals."
2.AdjectiveObscure, mysterious.
"arcane origins; arcane details"
3.AdjectiveRequiring secret or mysterious knowledge to understand.
4.AdjectiveExtremely old (e.g. interpretation or knowledge), and possibly irrelevant.